A battery pack may comprise a plurality of battery cells. The battery cells may be configured in parallel and series to provide a desired level of battery voltage at a desired amp-hour rating. Battery cells arranged in series increase battery voltage while battery cells arranged in parallel increase the amp-hour rating of the battery. When a battery cells are discharged battery cell voltage may decrease. On the other hand, when battery cells are charged battery cell voltage may increase. Thus, battery voltage can be used as an indication of an amount of charge stored in a battery cell so that a battery pack can be charged or discharged as is prudent, at least under some conditions.
To facilitate battery pack charging and discharging, it is possible to determine battery cell voltage via an analog to digital converter (ADC). However, an ADC requires a stable reference voltage to accurately determine a voltage of a battery cell. If the reference voltage drifts (e.g., changes) over time, voltage measurements made by an ADC of battery cell voltage may degrade in accuracy. Consequently, it may be difficult to provide an accurate battery cell voltage measurement. Further, it may be difficult to make an accurate determination of total battery pack voltage from individual battery cell voltage measurements made by an ADC. As a result, it may be desirable to limit battery pack charging and discharging to a reduced level so that the battery pack voltage is within a desired range.
The inventors herein have recognized the above issues and developed an approach to address them. Specifically, the inventors have developed a method for verifying a reference voltage for battery cell voltage monitoring, comprising: referencing a first analog to digital converter to a reference voltage; providing a band-gap voltage from the reference voltage; and indicating degradation of the reference voltage when the band-gap reference voltage varies from a predetermined voltage range.
By checking a reference voltage which supplies a voltage to an ADC that monitors battery cell voltages via a band-gap reference, it may be possible to determine whether or not the reference voltage is operating at a desired voltage so that limiting of battery pack charging and discharging due to a changing reference voltage may be reduced. Thus, when it is determined that the reference voltage is operating at a desired voltage, a higher level of confidence in ADC measurements may be achieved. In one example, the present description provides for monitoring the reference voltage via a band-gap voltage of a microcontroller. If a voltage of the band-gap voltage varies by more than a predetermined amount of voltage, a condition of degradation can be indicated to a battery pack management system. In this way, it is possible for a plurality of modules to indicate reference voltage degradation within a battery pack.
The present description may provide several advantages. In particular, the approach can assess reference voltage degradation via an internal temperature compensated band-gap voltage. Further, the approach can reduce system costs as a second reference voltage is not required to assess the reference voltage.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.